Automobile accidents kill or injure thousands of people annually. Safety belts are only effective if worn, and even then may be of limited use in certain types of collisions. Another type of safety system for a vehicle driver provides an inflatable air cushion, or a so-called "airbag", in the region of the steering wheel. The airbag is connected to a propellant charge, which is detonated via a sensor upon impact. The charge fills the bag with air, or other gas, thereby providing a cushion to soften the impending impact. A further air-cushion unit can also be attached to the dashboard for the front-seat passenger.
Currently used airbag systems are not without problems, however. For example, the release sensors constitute a safety risk since they can malfunction, releasing the propellant unexpectedly in non-collision situations. In known electrical sensors, there is also the need to check the electrical detonation circuits regularly, since faults, such as short-circuiting, ground contact and cutouts, can lead to the failure or malfunctioning of the air-cushion unit. Also, electrical connections, for example slip-ring connections to the moveable steering wheel, and the air-cushion unit mounted in the center of the steering wheel, are relatively expensive to produce and, in the event of an accident, can be destroyed even before the sensors are released.
Previously-used release sensors are "acceleration" sensors, which react to the collision deceleration in an accident. In order to function reliably, the sensors must be able to distinguish between situations in which there should be no release of the air cushion, such as fast operation decelerations due to hard braking and small minor accidents, and a serious head-on collision, wherein inflation of the air cushion should occur. The higher the acceleration values required for a release operation, the greater the safeguard against a release malfunction. However, sensors utilizing collision deceleration for release are not always able to satisfactorily distinguish between decelerations for which inflation should occur and those for which it should not.
A frequent effect of a sharp head-on collision is that the vehicle driver strikes the steering wheel with his head, despite having his safety belt fastened. This is caused by the sharp forward shift of the upper part of the body and the head and/or by the steering wheel being thrust into the passenger space via the steering column as a result of the impact. German Offenlegungsschrift 1,655,597 therefore proposes, in the event of a head-on collision, to pull the steering wheel away from the possible head impact region towards the dashboard by means of a cable guided via a deflection device.
In vehicles without a device for pulling away the steering wheel, the steering column together with the steering wheel can assume an upright position in a head-on collision, so that the air cushion is not inflated towards the upper part of the body of the vehicle driver, but possibly only meets the driver's head. There is therefore the danger of serious injury caused by the dipping of the upper part of the body.